The purpose of this investigation is to explore the identity of the various ground substance components in human cortical bone and their ultrastructural relationships with each other, with collagen and with mineral. This study employs a coordinated application of histochemical, electron microscopic (scanning and transmission) and energy dispersive x-ray microanalysis techniques involving both enzymatic and heavy metal tagging. It is hoped that the undergoing study will provide a better understanding of the role of ground substance components in osteoid formation, ossification and bone tissue maintenance.